Field of the Invention
The present invention relates to a technique for multiplexing information in an image.
Description of the Related Art
There has been conventionally proposed a technique of embedding information in a printed product so the information does not visually stand out (to be referred to as “invisible” hereinafter). This technique called a digital watermark or steganography has been developed rapidly in recent years.
Japanese Patent Laid-Open No. 2005-26797 discloses a method of adding a correction marker to provide geometric transformation resistance when a printed product is read by a scanner or camera apparatus, and executing printing.
However, according to Japanese Patent Laid-Open No. 2005-26797, there is a phenomenon of a field curvature aberration in which the edge portion of a printed product blurs if the central portion of the printed product is in focus at the time of close-up shooting. Especially, the edge portion of the printed product when the central portion of the printed product is in focus is largely influenced by not only the field curvature aberration but also other Seidel's aberrations, and it is thus impossible to acquire a satisfactory analysis image necessary to extract information. To satisfactorily acquire an image of the entire printed product, there is provided a method of performing appropriate focusing for each region of the printed product, and acquiring an analysis image by bracket shooting composition. However, for example, if a contrast AF (Auto Focus) method incorporated in many camera-equipped mobile phones and smartphones is used, an edge part necessary for AF does not always exist in the edge portion of an image, and it is often difficult to perform focusing.